In order to improve the characteristics of a MONOS (Metal Oxide Nitride Oxide Silicon) type of nonvolatile semiconductor storage device, which is a type of semiconductor device, for example, there is a demand for suppressing leaks from the charge accumulation film to the control gate electrode via the block insulating film at writing to the storage device. Also, for example, there is an important to suppress the injection of electrons from the control gate electrode to the charge accumulation film during erasing of the storage device. Furthermore, for example, there is an important to suppress the leakage of stored electrons from the charge accumulation film to the control gate electrode or the semiconductor substrate via the block insulating film or the tunnel insulating film during the charge retention period of the storage device.
These same properties are important for the FG (Floating Gate) type of nonvolatile semiconductor storage device.
Therefore, there is an important for a film that suppresses leakage, etc., in a tunnel insulating film and a block insulating film used in an MONOS type of nonvolatile semiconductor storage device, or in a tunnel insulating film and an interelectrode insulating film used in an FG-type nonvolatile semiconductor storage device, and furthermore in a tunnel insulating film, floating gate insulating film, and interelectrode insulating film, used in a double floating gate type nonvolatile semiconductor storage device that includes two layers of floating gate.